SBHA-FISHERIES LABORATORY. 411 
The main branch continues downward, still situated 
slightly nearer the right side of the animal, to enter the 
visceral mass, and branches are given oft to the digestive 
gland. On the right side of the aorta a vessel arises which 
reaches the surface in the median line above the base of 
the foot, along the upper side of which it passes just 
beneath the epidermis, to supply the foot with blood 
(fie. 17, A.p.). This vessel gives off branches to the 
lower lip and inner palps, as indicated in the figure. 
Returning to the main branch, this is continued by a 
smaller vessel which lies on the right side of the 
alimentary canal, and follows it in its course through the 
visceral mass, giving off small vessels to the ascending 
loop of the intestine and to the reproductive organs. 
There is another vessel of almost the same size which 
arises from the above, at about the level of the foot, and 
passing deeper into the visceral mass, bifurcates into two 
branches which pass along the left side of the descending 
loop of the intestine (fig. 14, A. v.). 
The Posterior Aorta (fig. 14, Ao. p.) is a large vessel 
which leaves the ventricle below the intestine and on its 
right side. It runs for a short distance along the right 
ventro-lateral side of the rectum, and then gives rise to 
three vessels, the Rectal Artery (fig. 14, A.7.), which runs 
alongside the rectum, supplying it to the end, and two 
much larger vessels. One is the Posterior Pallial Artery 
(ig. 14, A.p.p.), the most important artery to the 
mantle, which turns upwards at an acute angle and runs 
in the roof of the pericardium towards the hinge line; it 
then passes to the posterior angle of the hinge and 
bifureates, forming right and left Cireumpallial (fig. 14, 
A.c.) arteries, which pass round the extreme margin of 
the mantle lobes and communicate eventually with the 
much smaller anterior pallial arteries. 
